Antineutrino Flux Research Articles

Determination of β -decay feeding patterns of Rb88 and Kr88 using the Modular Total Absorption Spectrometer at ORNL HRIBF

Precise determination of ground-state feeding in the β decay of fission products is an important but challenging component in modeling reactor antineutrino flux and reactor decay heat. The Modular Total Absorption Spectrometer (MTAS) is a versatile NaI(Tl) detector array that determines the true β-decay pattern free from the pandemonium effect, including precise ground-state feeding intensities. In this paper, we report MTAS results of the β feeding intensities of Rb88 and Kr88, fission products with large cumulative yields in nuclear reactors. By comparing MTAS results with previous measurements, Rb88 provides a validation of MTAS's ability to determine ground-state feedings in β decays, while the precision of Kr88 ground-state feeding is improved when compared with the Evaluated Nuclear Structure Data File (ENSDF). The investigation of sources that contribute to β feeding branching uncertainties in MTAS experiments is discussed in detail. Lastly, the deconvolution of Rb88 decay spectra suggests that MTAS can distinguish an allowed β spectral shape from a first forbidden unique β spectral shape.1 MoreReceived 29 October 2021Accepted 15 April 2022DOI:https://doi.org/10.1103/PhysRevC.105.054312©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayNuclear structure & decaysProperties59 ≤ A ≤ 89TechniquesNuclear data analysis & compilationSpectrometers & spectroscopic techniquesNuclear Physics

Prompt electron and tau neutrinos and antineutrinos in the forward region at the LHC

Neutrino fluxes at high rapidity and at high energy are sensitive to QCD dynamics of heavy-flavor production in kinematic regions where measurements have not yet been made. The FASERν and SND@LHC experiments scheduled for Run 3 at the Large Hadron Collider (LHC) and the proposed Forward Physics Facility with a suite of experiments during the High-Luminosity LHC phase will probe neutrinos at high pseudorapidity. This short paper reports on recent evaluations of the prompt ντ+ν¯τ and νe+ν¯e double-differential cross sections in pp collisions at the LHC from the production and decays of Ds± and D±, respectively. For s=14 TeV, the double-differential neutrino energy and pseudorapidity distributions are evaluated at NLO QCD. Data tables with these predictions are presented. Future work needed to refine predictions of neutrino and antineutrino fluxes in the forward region at the LHC is discussed.

Study on pulse shape discrimination power of plastic scintillators

Nuclear reactor safeguard, based on detection of electron antineutrino flux and energy spectrum, is of great interests to both administrative agencies such as International Atomic Energy Agency (IAEA) and neutrino community. A dominant reaction channel of such detection is inverse beta decay (IBD), for which discrimination of gamma against neutron is critical. In this study, pulse shape discrimination (PSD) is used over plastic scintillator, for its ease of detector assembly, no risk of leakage, and high chemical stability. Using 22Na and 137Cs radioactive sources to calibrate the energy response of the whole system (data acquisition and materials), EJ200 and EJ426 scintillator combination is used as the discrimination setup. The figure of merit (FOM) can reach 9.13 ± 0.01, and could be adopted to build a reactor neutrino safeguard detector. In addition, the PSD of two kinds of plastic scintillators were compared. The FOM of the EJ276 plastic scintillator can reach 1.35 ± 0.01 at the energy threshold of 1 MeV gamma equivalent in comparison to 0.96 ± 0.01 of UPS-113NG at the same energy threshold.

Test of nuclear decay rate variation due to an antineutrino flux

Unexplained variations of the decay rate for weak interaction decays such as $\beta^{\pm}$-decay, electron capture, as well as strong interaction $\alpha$-decay have been reported. Some researcher interpreted these variations as caused by an unexplained fundamental interaction. The purpose of the paper is to review decay rate parameter variations experiments and place them into a common comparable context and to make decay parameter measurements at the level of 10$^{-5}$ in the presences of an antineutrino flux, $\sim 3 \times10^{12}$ $\overline{\nu} \, cm^{-2} \, sec^{-1}$, 6.5 meters from the High Flux Isotope Reactor(HFIR) reactor core having an on-off cycle time of $\sim$30 days. Two weak interaction decays, one via electron capture and the other via $\beta^-$ decay were selected because the final state and the time reverse state each contain a neutrino and anti-neutrino, covering arguments that the anti-neutrino flux may interact differently or not at all in one of the cases. The experiment searched for variation of the $^{54}_{25}$Mn, e$^-$ capture and $^{137}_{~55}$Cs, $\beta^-$ decay rate parameters. The measured variation in the decay rate parameters are found to be $\delta \lambda/ \lambda = (0.034\pm 1.38)\times 10^{-5}$ for $^{54}_{25}$Mn and $\delta \lambda/ \lambda = (0.67\pm 1.56)\times 10^{-5}$ for $^{137}_{~55}$Cs. These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a $68\%$ confidence level upper limit sensitivity for $^{54}_{25}$Mn, $\delta \lambda/ \lambda \leq 1.31\times10^{-5}$ or $\sigma \leq 1.29\times10^{-25}\,cm^{2}$ in cross section and for $^{137}_{~55}$Cs, $\delta \lambda/ \lambda \leq 2.23\times10^{-5}$ or $\sigma \leq 5.69\times10^{-27}\,cm^{2}$. These null or no observable effect measurements places cross-section upper limits $\sim 10^{4}$ times more sensitive than past experiments.

Constraining dark matter-nucleon scattering cross section by the background electron anti-neutrino flux data

Celestial objects such as stars and planets might be able to capture a large amount of dark matter particles through dark matter-nucleon scattering. Many previous studies have considered different celestial objects such as the Sun and the Earth as natural dark matter detectors and obtained some stringent bounds of the dark matter-nucleon scattering cross section. In this study, we use the ∼10 MeV electron neutrino flux limits obtained by the Super-Kamiokande experiment and consider the Earth as a large natural dark matter detector to constrain the dark matter-nucleon scattering cross section. We show that this method can generally get more stringent limits. For certain ranges of dark matter mass annihilating via the bb¯ channel, the limits of cross section for the isospin-independent scattering and proton-only scattering could be more stringent than that obtained in the PICO direct-detection experiment.

Measurement of reactor antineutrino flux and spectrum at RENO

The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos\,($\overline{\nu}_e$) from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966\,094\,(116\,111)\,$\overline{\nu}_e$ candidate events with a background fraction of 2.39\%\,(5.13\%), acquired in the near\,(far) detector, from August 2011 to March 2020. The inverse beta decay (IBD) yield is measured as (5.852$\,\pm\,$0.124$) \times 10^{-43}$\,cm$^2$/fission, corresponding to 0.941\,$\pm$ 0.019 of the prediction by the Huber and Mueller (HM) model. A reactor $\overline{\nu}_e$ spectrum is obtained by unfolding a measured IBD prompt spectrum. The obtained neutrino spectrum shows a clear excess around 6\,MeV relative to the HM prediction. The obtained reactor $\overline{\nu}_e$ spectrum will be useful for understanding unknown neutrino properties and reactor models. The observed discrepancies suggest the next round of precision measurements and modification of the current reactor $\overline{\nu}_e$ models.

Exploring CEνNS of reactor neutrinos with the NUCLEUS experiment

Coherent elastic neutrino-nucleus scattering (CEνNS) offers a unique way to study neutrino properties and to search for new physics beyond the Standard Model. The NUCLEUS experiment aims to measure CEνNS of reactor anti-neutrinos down to unprecedented low nuclear recoil energies. The novel gram-scale cryogenic detectors feature an ultra-low energy threshold of ≤20eVnr and a rise time of a few 100 μs which allows the operation above ground. The fiducialization of the detectors provides an effective discrimination of ambient γ- and surface backgrounds. Furthermore, the use of multiple targets promises a high physics potential. The NUCLEUS experiment will be located at a new experimental site at the Chooz nuclear power plant in France, providing a high anti-neutrino flux of . The commissioning of the experimental setup with a comprehensive background measurement is planned for 2022.

The Stereo search for a sterile neutrino at the ILL reactor with full data sample

During the last decades, several parameters describing the neutrino oscillation phenomenon have been characterized thanks to reactor neutrino experiments, in particular the precise measurement of the last-to-be-measured mixing angle θ 13. Following a reactor antineutrino flux re-estimation in 2011, a 6% deficit between observed and predicted reactor antineutrino fluxes, known as the Reactor Antineutrino Anomaly, has been observed. The Reactor Antineutrino Anomaly could be explained by an oscillation toward an additional non-interacting, (thus “sterile”) neutrino. The parameters that best explain the RAA are a mixing angle value of sin2 (2θnew ) = 0.17 and a mass splitting value of . Additionally, a discrepancy between the measured and predicted antineutrino energy spectrum taking the form of an excess of events around 5 MeV has been observed by several reactor neutrino experiments. This discrepancy has yet to be fully understood but could be caused by incorrect predictions of the neutrino spectra. The STEREO experiment, located at Institut Laue-Langevin in Grenoble (France), was designed to test the above mentioned oscillation hypothesis independently of shape and rate predictions. The segmented detector, located at ∼10 m of a compact reactor core, allows for a measurement of the antineutrino energy spectrum at various baselines, sensitive to the oscillation toward a sterile neutrino that would distort the spectrum differently at each baseline. The experiment could also help to disentangle isotopic contributions to the neutrino energy spectrum by providing a measurement of the spectrum shape and rate originating from a core with highly enriched (93%)235U. The experiment took data between November 2016 and November 2020. This talk will present the latest limits set in the oscillation parameter space with the full data sample, amounting to 334 (544) days of reactor-on (off), as well as the updated rate and spectrum shape measurements.

Study of Ocean Bottom Detector for observation of geo-neutrino from the mantle

Observation of anti-neutrinos emitted from radioactive isotopes inside Earth(geo-neutrinos) brings direct information on the Earth’s chemical composition and its heat balance, which strongly relate to the Earth’s dynamics. To date, two experiments (KamLAND and Borexino) have measured geo-neutrinos and constrained the range of acceptable models for the Earth’s chemical composition, but distinguishing the mantle flux by land-based detectors is challenging as the crust signal is about 70% of the total anti-neutrino flux. Given the oceanic crust is thinner and has lower concentration of radioactive elements than continental crust, geo-neutrino detector in the ocean, Ocean Bottom Detector (OBD), makes it sensitive to geo-neutrinos originating from the Earth’s mantle. Our working group was jointly constructed from interdisciplinary communities in Japan which include particle physics, geoscience, and ocean engineering. We have started to work on technological developments of OBD. We are now developing a 20 kg prototype liquid scintillator detector. This detector will undergo operation deployment tests at 1 km depth seafloor in 2022.

Radioactivity control strategy for the JUNO detector

JUNO is a massive liquid scintillator detector with a primary scientific goal of determining the neutrino mass ordering by studying the oscillated anti-neutrino flux coming from two nuclear power plants at 53 km distance. The expected signal anti-neutrino interaction rate is only 60 counts per day (cpd), therefore a careful control of the background sources due to radioactivity is critical. In particular, natural radioactivity present in all materials and in the environment represents a serious issue that could impair the sensitivity of the experiment if appropriate countermeasures were not foreseen. In this paper we discuss the background reduction strategies undertaken by the JUNO collaboration to reduce at minimum the impact of natural radioactivity. We describe our efforts for an optimized experimental design, a careful material screening and accurate detector production handling, and a constant control of the expected results through a meticulous Monte Carlo simulation program. We show that all these actions should allow us to keep the background count rate safely below the target value of 10 Hz (i.e. ∼1 cpd accidental background) in the default fiducial volume, above an energy threshold of 0.7 MeV.

Status of Anomalies and Sterile Neutrino Searches at Nuclear Reactors

Two anomalies at nuclear reactors, one related to the absolute antineutrino flux, one related to the antineutrino spectral shape, have drawn special attention to the field of reactor neutrino physics during the past decade. Numerous experimental efforts have been launched to investigate the reliability of flux models and to explore whether sterile neutrino oscillations are at the base of the experimental findings. This review aims to provide an overview on the status of experimental searches at reactors for sterile neutrino oscillations and measurements of the antineutrino spectral shape in mid-2021. The individual experimental approaches and results are reviewed. Moreover, global and joint oscillation and spectral shape analyses are discussed. Many experiments allow setting of constraints on sterile oscillation parameters, but cannot yet cover the entire relevant parameter space. Others find evidence in favour of certain parameter space regions. In contrast, findings on the spectral shape appear to give an overall consistent picture across experiments and allow narrowing down of contributions of certain isotopes.

Constraints on decaying sterile neutrinos from solar antineutrinos

Solar neutrino experiments are highly sensitive to sources of $\nu\to\overline{\nu}$ conversions in the $^8$B neutrino flux. In this work we adapt these searches to non-minimal sterile neutrino models recently proposed to explain the LSND, MiniBooNE, and reactor anomalies. The production of such sterile neutrinos in the Sun, followed the decay chain $\nu_4 \to \nu \phi \to \nu \nu \overline{\nu}$ with a new scalar $\phi$ results in upper limits for the neutrino mixing $|U_{e4}|^2$ at the per mille level. We conclude that a simultaneous explanations of all anomalies is in tension with KamLAND, Super-Kamiokande, and Borexino constraints on the flux of solar antineutrinos. We then present other minimal models that violate parity or lepton number, and discuss the applicability of our constraints in each case. Future improvements can be expected from existing Borexino data as well as from future searches at Super-Kamiokande with added Gd.

IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data

The IceCube Neutrino Observatory has established the existence of a high-energy all-sky neutrino flux of astrophysical origin. This discovery was made using events interacting within a fiducial region of the detector surrounded by an active veto and with reconstructed energy above 60 TeV, commonly known as the high-energy starting event sample (HESE). We revisit the analysis of the HESE sample with an additional 4.5 years of data, newer glacial ice models, and improved systematics treatment. This paper describes the sample in detail, reports on the latest astrophysical neutrino flux measurements, and presents a source search for astrophysical neutrinos. We give the compatibility of these observations with specific isotropic flux models proposed in the literature as well as generic power-law-like scenarios. Assuming νe:νμ:ντ=1:1:1, and an equal flux of neutrinos and antineutrinos, we find that the astrophysical neutrino spectrum is compatible with an unbroken power law, with a preferred spectral index of 2.87−0.19+0.20 for the 68% confidence interval.27 MoreReceived 16 November 2020Accepted 29 April 2021DOI:https://doi.org/10.1103/PhysRevD.104.022002© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic ray & astroparticle detectorsParticle astrophysicsGravitation, Cosmology & Astrophysics

Chiral selection, isotopic abundance shifts, and autocatalysis of meteoritic amino acids

The discovery of amino acids in meteorites has presented two clues to the origin of their processing subsequent to their formation: a slight preference for left-handedness in some of them, and isotopic anomalies in some of their constituent atoms. In this article we present theoretical results from the Supernova Neutrino Amino Acid Processing (SNAAP) model, which uses electron anti-neutrinos and the magnetic fields from source objects such as supernovae or colliding neutron stars to selectively destroy one amino acid chirality and to create isotopic abundance shifts. For plausible magnetic fields and electron anti-neutrino fluxes, non-zero, positive enantiomeric excesses, $ee$s, defined to be the relative left/right asymmetry in an amino acid population, are reviewed for two amino acids, and conditions are suggested that would produce $ee>0$ for all of the $\alpha$-amino acids. The relatively high energy anti-neutrinos that produce the $ee$s would inevitably also produce isotopic anomalies. A nuclear reaction network was developed to describe the reactions resulting from them and the nuclides in the meteorites. At similar anti-neutrino fluxes, assumed recombination of the detritus from the anti-neutrino interactions is shown to produce appreciable isotopic anomalies in qualitative agreement with those observed for D/$^1$H and $^{15}$N/$^{14}$N. The isotopic anomalies for $^{13}$C/$^{12}$C are predicted to be small, as are also observed. Autocatalysis may be necessary for any model to produce the largest $ee$s observed in meteorites. This allows the constraints of the original SNAAP model to be relaxed, increasing the probability of meteoroid survival in sites where amino acid processing is possible. These results have obvious implications for the origin of life on Earth.

Coherent elastic neutrino nucleus scatter response of semiconductor detectors to nuclear reactor antineutrinos

We studied the performance of advanced semiconductor detectors to measure reactor antineutrino with the potential to drastically improve efficiency and lower existing thresholds of detectable incident-antineutrino-energy. Recent developments, such as those by the Mitchell Institute Neutrino Experiment at Reactor (MINER) experiment at Texas A&M University, in semiconductor technologies have enabled the ability to lower the coherent-elastic-neutrino-nucleus-scatter (CEνNS) based detection threshold to nuclear recoil energies between 10-eV and 100-eV (Dutta et al., 2016). Existing detectors based on inverse beta decay (IBD) have a threshold of 1.806 MeV (Oralbaev et al., 2016). In this study, we calculated the CEνNS response of semiconductor detectors to antineutrino flux from a 1-MW(th) TRIGA reactor as a function of incident antineutrino energy. In the calculations, the reaction rates of detectors made of germanium and silicon are calculated for a 100-kg detector and placed 10 m from the core. No background radiation characterization and reduction were performed. First, the reactor antineutrino flux spectrum is obtained for the fuel composition specific to 1-MW(th) TRIGA reactor without any thresholds. Next, the standard model (SM) of physics is used to calculate the CEνNS cross-section as a function of incident antineutrino energy. Finally, the above two functions are convolved to provide the detector response for both, germanium and silicon detectors. The results show that germanium has a greater efficiency than silicon; however, it is shown that silicon is sensitive to lower antineutrino energies. It is found that a 100-eV nuclear recoil in germanium semiconductor detectors can be produced by a minimum incident energy of 1.84 MeV antineutrinos, and in silicon by 1.14 MeV antineutrinos. For the lower threshold, a 20-eV nuclear recoil in germanium semiconductors can be produced by a minimum incident energy of 0.82 MeV antineutrinos and in Si by 0.51 MeV antineutrinos. Lowering the detector response energy sensitivity equips us with newer techniques for nuclear fuel monitoring.

Prospects of detecting the reactor $$\overline{\nu }_{\mathrm{e}}$$-Ar coherent elastic scattering with a low-threshold dual-phase argon time projection chamber at Taishan

We propose to measure the coherent elastic neutrino nucleus scattering (CE$\nu$NS) using a dual-phase liquid argon time projection chamber (TPC) with 200kg fiducial mass. The detector is expected to be adjacent to the JUNO-TAO experiment and to be about 35m from a reactor core with 4.6GW thermal power at Taishan. The antineutrino flux is approximately 6$\times10^{12}$cm$^{-1}$s$^{-1}$ at this location, leading to more than 11,000 coherent scattering events per day in the fiducial mass. However, the nuclear recoil energies concentrate in the sub-keV region, corresponding to less than ten ionisation electrons in the liquid argon. The detection of several ionisation electrons can be achieved in the dual-phase TPC due to the large amplification in the gas region. With a feasible detection threshold of four ionisation electrons, the signal rate is 955 per day. The detector is designed to be shielded well from cosmogenic backgrounds and ambient radioactivities to reach a 16% background-to-signal ratio in the energy region of interest. With the large CE$\nu$NS sample, the expected sensitivity of measuring the weak mixing angle $\sin^{2}\theta_{W}$, and of limiting the neutrino magnetic moment are discussed. In addition, a synergy between the reactor antineutrino CE$\nu$NS experiment and the dark matter experiment is foreseen.

Large-size sub-keV sensitive germanium detectors for the CONUS experiment

Intense fluxes of reactor antineutrinos offer a unique possibility to probe the fully coherent character of elastic neutrino scattering off atomic nuclei. In this regard, detectors face the challenge to register tiny recoil energies of a few keV at the maximum. The Conus experiment was installed in 17.1 m distance from the reactor core of the nuclear power plant in Brokdorf, Germany, and was designed to detect this neutrino interaction channel by using four 1 kg-sized point contact germanium detectors with sub-keV energy thresholds. This report describes the unique specifications addressed to the design, the research and development, and the final production of these detectors. It demonstrates their excellent electronic performance obtained during commissioning under laboratory conditions as well as during the first 2 years of operation at the reactor site which started on April 1, 2018. It highlights the long-term stability of different detector parameters and the achieved background levels of the germanium detectors inside the Conus shield setup.

The physics potential of a reactor neutrino experiment with Skipper CCDs: measuring the weak mixing angle

We analyze in detail the physics potential of an experiment like the one recently proposed by the vIOLETA collaboration: a kilogram-scale Skipper CCD detector deployed 12 meters away from a commercial nuclear reactor core. This experiment would be able to detect coherent elastic neutrino nucleus scattering from reactor neutrinos, capitalizing on the exceptionally low ionization energy threshold of Skipper CCDs. To estimate the physics reach, we elect the measurement of the weak mixing angle as a case study. We choose a realistic benchmark experimental setup and perform variations on this benchmark to understand the role of quenching factor and its systematic uncertainties, background rate and spectral shape, total exposure, and reactor antineutrino flux uncertainty. We take full advantage of the reactor flux measurement of the Daya Bay collaboration to perform a data driven analysis which is, up to a certain extent, independent of the theoretical un- certainties on the reactor antineutrino flux. We show that, under reasonable assumptions, this experimental setup may provide a competitive measurement of the weak mixing angle at few MeV scale with neutrino-nucleus scattering.

SoLid: a short baseline reactor neutrino experiment

The SoLid experiment, short for Search for Oscillations with a Lithium-6 detector, is a new generation neutrino experiment which tries to address the key challenges for high precision reactor neutrino measurements at very short distances from a reactor core and with little or no overburden. The primary goal of the SoLid experiment is to perform a precise measurement of the electron antineutrino energy spectrum and flux and to search for very short distance neutrino oscillations as a probe of eV-scale sterile neutrinos. This paper describes the SoLid detection principle, the mechanical design and the construction of the detector. It then reports on the installation and commissioning on site near the BR2 reactor, Belgium, and finally highlights its performance in terms of detector response and calibration.

Ab initio calculations of reactor antineutrino fluxes with exact lepton wave functions

New ab initio calculations of the isotopic reactor antineutrino fluxes are provided with exact numerical calculations of the lepton wave functions, assuming all the decay branches are allowed GT transitions. We illustrate that the analytical Fermi function and finite size effect each could have the largest spectral deviation of O(10%), whereas the effect of their combination could result in spectral deviations at the level of 5%—10%. Meanwhile, we also find that several forms of the extended charge distributions have negligible effects on the spectral variation. Using the state-of-the-art nuclear databases, compared to usual ab initio calculations using the analytical single beta decay spectrum, our new calculation shows sizable but opposite spectral deviations at the level of 2%—4% for the cumulative antineutrino and electron energy spectra which may partially contribute to the observed spectral excess in the high energy antineutrino range. Finally we observe that the bias of analytical beta decay spectrum approximation is rather universal for all the four fissionable isotopes.